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1 Deakin Research Online This is the published version: Mendoza, J., Watson, K., Cerin, E., Nga, N.T., Baranowski, T. and Nicklas, T. 2009, Active commuting to school and association with physical activity and weight status among US youth, in Proceedings of the 2009 Active Living Research conference, The Conference, San Diego, Calif., pp Available from Deakin Research Online: Reproduced with the kind permission of the copyright owner. Copyright: 2009, Active Living Research Conference.

2 Active Commuting to School and Association with Physical Activity and Adiposity among US Youth Jason A. Mendoza, MD, MPH Assistant Professor of Pediatrics USDA/ARS Children s Nutrition Research Center and Academic General Pediatrics, Baylor College of Medicine

3 Background Increasing childhood physical activity (PA) to prevent childhood obesity Healthy People 2010 American Heart Association American Cancer Society 2008 Physical Activity Guidelines for Americans

4 Decline in Physical Activity Average Weekday and Weekend Minutes of MVPA by Gender Nader, P. R. et al. JAMA 2008;300:

5 Active Commuting to School (ACS) ACS and PA: 28 more minutes MVPA (Lee 2008) Self/parent reported PA (16 of 25 studies) ACS and adiposity: mixed findings Compensation for increased PA of ACS by decreasing other types of PA? Limitations of previous studies: Small or regional samples PA subjectively measured by recall None controlled for dietary energy intake

6 Hypotheses 1. ACS positively related to MVPA 2. ACS inversely related to adiposity

7 NHANES Continuous series of cross-sectional surveys conducted by CDC Complex, stratified, multistage, probability cluster sampling design Nationally representative sample of the civilian, non-institutionalized US population Surveillance for Healthy People 2010

8 Methods Subjects Inclusion: years old (in school) Age range for questions on ACS Main outcome measures (adiposity) BMI-z score sum of triceps + subscapular skinfolds (mm)

9 Outcomes MVPA: Accelerometers (Actigraph 7164) Valid Day: >10 hours of wear Data used if >4 valid days of wear 1-min epochs MVPA threshold set at 4 METs Mean total min. MVPA/day Before- and after school min. MVPA/day: Mon-Fri 6:30 to 9 am and 2:30 to 4 pm *Troiano et al 2008

10 Covariates Age Gender Race/ethnicity Poverty to income ratio Dietary energy intake (kcal) Mean of two, 24-hour dietary recalls using USDA Automated Multiple Pass Method

11 Main Exposure: ACS (min/d) Over the past 30 days, have you walked or bicycled as part of getting to and from work, or school, or to do errands? (yes/no) Over the past 30 days, how often did you do this? (times per day, week, month) On those days when you walked or bicycled, about how long did you spend altogether doing this? (minutes)

12 Analyses: DV=MVPA Multivariate linear regression Independent variable: ACS Dependent variable: MVPA (total daily or before- and after-school) Covariates: sociodemographics and energy intake (kcal)

13 Analyses: DV=Adiposity Multivariate linear regression Independent variable: ACS Dependent variable: BMI-z score or skinfolds Covariates: sociodemographics and energy intake (kcal) α = 0.05 for significance

14 Participants Characteristics n % (SE) Gender Female (1.7) Race/Ethnicity Non-Hispanic White (5.2) Non-Hispanic Black (2.3) Hispanic (3.1) Other (2.0) n M (SE) Age (years) (0.1) Poverty to Income Ratio (0.1) Average Energy Intake (kcals) 789 2,211 (42) BMI z-score (0.1) Waist Circumference (cm) (0.7) Skinfolds (Triceps + Subscapular; mm) (0.9) ACS (min/day) (1.6) Average weekly MVPA (min/day) (2.0) Weekday average MVPA min before/after school (0.9)

15 Results: Daily min. MVPA MVPA (min) R 2 =0.31, p= Active Commuting (min/day) *controlling for age, gender, race/ethnicity, and income, and energy intake

16 Results: Skinfolds 30.5 Skinfolds (mm) R 2 =0.12, p= Active Commuting (min/day) *controlling for age, gender, race/ethnicity, and income, and energy intake

17 Results: BMI-z score 0.7 BMI-z score R 2 =0.05, p= Active commuting (min/d) *controlling for age, gender, race/ethnicity, and income, and energy intake

18 Strengths Nationally representative sample Objective measure of physical activity Controlled for energy intake (kcal) MVPA model R 2 = 0.31

19 Limitations Cross-sectional No data on distance from school, built environment, neighborhood safety Main exposure assessed by recall

20 Implications ACS as potential means to broadly improve physical activity and prevent obesity among US youth Need for RCTs to assess ACS and impact on physical activity and adiposity

21 Acknowledgements Kathy Watson and Nga Nguyen (statistics) Collaborators: Ester Cerin, PhD, Tom Baranowski, PhD, and Theresa Nicklas, DrPH Colleagues and staff in CNRC and Academic General Pediatrics, Baylor College of Medicine Funding: USDA

22 Presentations Active Commuting to School and Association with Physical Activity and Adiposity among US Youth February, 2009 Author: Jason Mendoza, M.D., M.P.H., Kathy Watson, M.S., Ester Cerin, Ph.D., Tom Baranowski, Ph.D., & Theresa Nicklas, Dr.P.H. Topic: Schools, Walking and Biking to School Population Served: African American, Latino/Hispanic, Multiple Race/Ethnic Sample, School-age Youth (K-12), White Location by State: National Study Type: Correlates DOWNLOAD Description: Presentation at the 2009 Active Living Research Annual Conference Background: Studies have reported inconsistent findings for the relationship between active commuting to school (ACS) and physical activity or weight status/adiposity among youth. These mixed findings may be due to reliance on self-report measures of physical activity, samples drawn from specific populations, inadequate statistical power, or lack of data on dietary energy intake, which may confound the relationship. No reports have examined physical activity as a mediator of active commuting and weight status/adiposity. Objectives: To examine (1) the relationship between ACS and weight status/adiposity and (2) whether moderate-to-vigorous physical activity (MVPA) mediates the relationship between ACS and weight status/adiposity among a nationally representative sample of US youth. Methods: We conducted a cross-sectional analysis using multiple linear regression models on a nationally representative sample of participants aged years from NHANES, (n=827 unweighted, n= 15,946,216 weighted). The main exposure variable of ACS was assessed by recall of walking or bicycling as part of getting to and from school over the past 30 days. Anthropometric measurements (height and weight for BMI-z, waist circumference, skinfold thicknesses [sum of subscapular and triceps]) were obtained using standardized techniques and equipment. Physical activity was objectively measured by

23 accelerometers, using 1-minute epochs. Besides overall daily MVPA, we also examined the subset of before- and afterschool MVPA (Mon - Fri: 6:30-9 am and 2:30-4 pm). Dietary energy intake was a covariate and calculated from the mean of two 24-hour recalls. Other covariates included age, gender, race/ethnicity, and poverty-to-income ratio. We used the product-of-coefficients method to test for mediation. Results: 32.9% of participants aged years actively commuted to school at least two days per week. In multivariate models, controlling for age, gender, race/ethnicity, poverty-to-income ratio, and energy intake, ACS was inversely associated with BMI-z score (std. beta=-0.08, p=0.040, R 2 =0.06) and skinfold thicknesses (std. beta=-0.06, p=0.033, R 2 =0.13). ACS was positively associated with overall daily MVPA (std. beta=0.11, p=0.039, R 2 =0.28) and with before- and after-school MVPA (std. beta=0.20, p<0.001, R 2 =0.22). Before- and after-school MVPA significantly mediated the relationship between ACS and waist circumference (p=0.03) and skinfold thicknesses (p=0.03). Total minutes of MVPA mediated no relationships. Conclusions: Among a nationally representative sample of US youth, active commuting to school was associated with lower BMI-z and adiposity. Additionally, those who actively commuted to school achieved greater MVPA. Before- and after-school MVPA was a mediator between ACS and measures of obesity and body fatness. ACS appears to be an important behavior to target for population-based physical activity promotion and obesity prevention interventions. Support: US Department of Agriculture Current Research Information System RELATED TOOLS & RESOURCES All Tools & Resources Pilot and Feasibility Evaluation of a Walking School Bus Policy Intervention for Elementary School Students Document Type: Project Profile Topics: Schools, Safe Routes to School, Walking and Biking to School